Nowadays an enormous amount of electric energy power is transported and consumed. A current trend is to buy electricity where it is cheapest, resulting in an enormous amount of electricity transport over large distances by using the existing electricity distribution network.
Because the capacity of the existing electricity distribution network is getting insufficient, it should be upgraded in the near future.
An obvious solution could be building new additional electric power transmission lines, but economical and ecological reasons prevent this in a lot of cases.
Another solution could be increasing the amount of electrical current flowing through the existing lines. However, as heat generation increases quadratic with the current, the nominal operating temperature rises then from about 50° C. up to about 200° C. and even 300° C. The existing electric power transmission lines equipped with traditional ACSR (aluminum conductor steel reinforced) cables are not suitable for operating at these temperatures. With rising temperatures, the conductors (mostly aluminum) which also partially mechanically support the cable, loose their mechanical strength leading to significant sag. In addition, the zinc of the galvanized steel wires of the core diffuses and forms a brittle iron-zinc layer causing flaking and decreasing corrosion resistance. In case of ACSS (aluminum conductor steel supported) cables, where the aluminum conductors do not mechanically support the cable, thermal expansion of the steel core leads to significant sag at high operating temperatures.
Another solution could lie in using an increased conductor section to increase the conductor current carrying capacity. This would obviously result in increased cable diameter, thereby increasing ice and wind loading. Higher ice and wind loading increases pole/tower loading and oblige shorter design spans. To be able to increase the conductor section without increasing the cable diameter, trapezoidal shaped wires and compacting techniques are used to compact the conductor section.
As described in “Transmission conductors—A review of the design and selection criteria” by Southwire Communications (Jan. 31, 2003), compact conductors can be manufactured by passing the stranded cable through powerful compacting rolls or a compacting die. Another technique as described is stranding trapezoidal shape wired conductors. Their shape results also in less void area in between the conductors and a reduced cable diameter.
However, since electricity consumption is still increasing, the need is clearly felt for an electric transmission cable either with the same cable diameter compared to the existing electric transmission cables, but having an increased conductor current carrying capacity, either with a smaller cable diameter, but keeping at least the same conductor current carrying capacity. Furthermore, the load carrying core should have at least the same tensile strength as compared to conventional cores and at least the same corrosion resistance.
In accordance with the present invention, an improved core for electric transmission cable and method of fabricating it is now presented to overcome all drawbacks of the prior art and to fulfill this need.